====== Week 4 ======

~~NOTOC~~


===== Lecture Notes =====

**Critical Sections**

  * Recap from last week:
    * UPC setup, including ssh keys and script to compile/run
    * Finish up demo of last two versions of UPC temperature programs
    * vim questions? tips/advice?
    * Programming assignment 2 due: next Tue, Feb 17 

  * Ben-Ari Ch 3 
    * slides: {{slides.pdf|PDF}}
      * begin slide 3.1, p. 50
    * The approaches to enter and exit critical sections were low-level and brittle
      * low-level because:  relied on busy-waiting and checking on global variables
      * brittle because:  many reasons!  
        * processes relied on each other to enter their own CS!
        * hard-coded for a specific number of processes (i.e., 2)!  what about for n?

** Class Exercise **

  * **More practice with interleavings**
    * (Adapted from Problem 2.19 from Andrews's MPD text)
    * {{mpd-2.19-interleavings.pdf|mpd-2.19-interleavings.pdf}}  (handout)


**Semaphores**

  * Next we introduce the abstraction of semaphores to control access to CS
  * Ben-Ari Ch 6
    * slides: {{slides.pdf|PDF}}
      * begin slide 6.1, p. 111


===== Homework =====

  * Written HW: Ben-Ari p. 39: 
    * Exercises 2, 3, and 4
    * Haven't forgotten that I owe you feedback--sorry!

 
===== Programming Assignment 2 =====

  * UPC Exercises 1.1 through 1.7
  * Due: Tue, Feb 17, 11:59pm
  * Here's a link: [[https://www.cs.vassar.edu/~cs377/private/|private]]